Linear alkylbenzenes (LAB) have been the surfactant of choice because they are cost effective and biodegradable. Sulfonates of LAB are the main ingredients in detergent powders. In the present day art, LABs are manufactured by the alkylation of benzene by linear olefins in the presence of HF acid. U.S. Pat. Nos. 3,494,970 and 3,830,865 describe a process for the production of LAB using HF catalysts. U.S. Pat. Nos. 3,631,123 and 3,674,885 and 3,703,559 describe the use of other Lewis acid catalysts such as AlCl.sub.3 in the production of LAB. In addition to the use of the above liquid phase acid catalysts, solid acid catalysts such as clays and zeolites have also been used in the production of LAB. U.S. Pat. No. 4,459,426 describes the use of zeolites as the catalysts for the alkylation of benzene with light C.sub.2 -C.sub.4 olefins. Due to the narrow size of the zeolite pores, they do not allow the diffusion of heavy olefins. Thus the alkylation in the presence of the said zeolites can only be carried out with light olefins. U.S. Pat. No. 3,849,507 describes the use of a clayish material activated with mineral acids and subsequently made into pellets for alkylation of benzene with olefins with 4 to 8 carbon atoms per olefin molecule. U.S. Pat. No. 4,046,826 uses a natural or synthetic trioctahedral clay, hectorite type, interchanged with metallic cations for the alkylation of benzene with heavy olefins, basically 1-dodecene. European Patent application 83970 uses for the alkylation of benzene with light olefins a clay in which pillars of alumina have been anchored inside its laminar structure, as catalyst. U.S. Pat. No. 3,417,148 refers to the use of a crystalline aluminosilicate chemically combined with metallic subfluoride as a catalyst for the production of alkylbenzenes. U.S. Pat. No. 4,070,407 and assigned to Mobil Oil Co. describes the use of a crystalline aluminosilicate zeolite as a catalyst for the alkylation of benzene with olefins, alcohols and alkyl halides to produce alkylbenzenes. European Patent application Eu.0,353,813 Al describes a process for the alkylation of benzene with C.sub.2 -C.sub.20 mono-olefins in the presence of an aluminium-magnesium silicate catalyst to give LAB of detergent range. The process is continuously carried out in a fixed bed, the alkylation taking place in the liquid phase.
In the present art, the process using liquid HF acid as the alkylation catalyst is in commercial practice in most of the plants all around the world. In the process developed by E. R. Fenske, U.S. Pat. No. 3,494,971 assigned to UOP Company, the alkylation takes place in successive steps and uses HF as a catalyst either fresh and/or regenerated depending on the different steps of the process. The feeding of liquid hydrocarbons (10 to 15 carbon atoms per molecule) is made up of a mixture of an excess (90%) of non-dehydrogenated linear hydrocarbons alone with a minor olefin fraction (10%) with approximately 95% mono-olefins and 5% diolefins. Benzene is in molar excess over the mono-olefin fraction. Two phases are obtained as the reaction product, the one which contains the alkylation catalyst and the other one that contains the hydrocarbons. From the reaction product the HF catalyst is separated/partly regenerated and recycled. Benzene is also separated and recycled to the alkylation reactor. The unreacted linear paraffins are separated from the LAB and recycled to the dehydrogenation reactor for partial conversion to linear olefins.
There are a few limitations in the prior-art processes using liquid phase acid catalysts such as HF, AlCl.sub.3 etc. One limitation is the corrosive nature of these acids leading to laborious and costly procedures and equipment for their handling. A second limitation is the environmental hazards in the handling and disposal of the spent HF catalyst. A third limitation is the toxicity of the HF acid to the plant personnel in case of leaks due to accidental plant upsets.
The use of prior-art solid acid catalysts such as zeolites and clay material also has limitations. A major limitation in the use of such catalysts is the very short cycle length between regenerations necessitating frequent interruptions in the production of LAB. For example, in the European Patent application EU 0,353,813 assigned to Petrosa, Example 1 cites the normal operating cycle length of the catalyst as 12 hrs. The regeneration of the catalyst is carried out in a semi-continuous manner making alternating and successive currents of paraffins and alcohols pass through the catalyst in cycles. The duration of the regeneration cycle was cited as 6 hrs.
In view of the above, it was the objective of the work leading to the present invention to discover a process for the manufacture of LAB using solid catalysts under conditions wherein the catalyst is not deactivated and hence leading to normal operating cycle lengths between successive regenerations which are substantially longer than those prevailing in the prior-art.